The immediate objective of this research is to improve the models of iron-sulfur proteins already solved and determine the structures of desulforedoxin and ferredoxin II, both from Desulfovibrio gigas. The methods to be used are those of single crystal X-ray diffraction, including crystallographic refinement of models based on multiple isomorphous replacement or derived by application of the rotation function. The long-range objective of this work is to provide a structural basis for understanding the properties and function of iron-sulfur proteins.